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Controlling jet engine thrust on airliners
Passenger jet airliners seem to control thrust by just adjusting the amount of fuel going to the engine thus affecting the engine rpm. This means it takes a small amount of time to spool up from minimum to maximum throttle and vice versa.
Are there any attempts to allow faster thrust response than this? Are any in current or planned use?

It seems that one could control the compressor pitch, change the gear ratio, or adjust the bypass ratio -- but I'm not sure anyone is doing this. Afterburners and thrust reversers/vectoring don't count. Faster engine respond would help with situations such as loss of rudder control let alone other emergency situations.

Related

Well... one thing you really don't want a lot of on an airliner is acceleration, in any direction, so I really don't see this as much of an issue.  The more that gravity feels like it's pointing at the floor, the better for all concerned.  You don't exactly want a passenger craft to crank into full reheat, sending the refreshment cart blasting down the aisle and out the tail.

You most certainly can NOT change the bypass ratio or gear ratio (assuming fan has gearbox) mid flight! Also as far as I know there are no variable pitch compressors. The extra mechanics would add a lot of weight for little gain.

Faster engine response would help with situations such as loss of rudder control.

Throttle originally means a flap that restricts amount of air going to the engine and that is specific to spark-ignition piston engines.

Edited question to fix my use of terminology.

I don't think this is a duplicate of the other question, which is very specific. Think of a question on a search engine that would lead to both questions.

Are there any attempts to allow faster thrust response than this? Are any in current or planned use?

First, for turbine engines, the more often used term is thrust lever or power lever rather than throttle. You can Google "throttle vs thrust lever" for that discussion.
I'll use the 727 and the 747 to illustrate what was done prior to when I retired in 1999.
In initial 727-100 sim training, the instructor had us bring the power levers all the way back and allow the descent to stabilize in landing configuration at full flaps. Then, at a given altitude the instructor would tell us to start climbing, at which time we would advance the thrust levers to max power and clean up. From that moment, we would lose hundreds of feet before the aircraft started to climb. The primary reason for the delay was that the engines took 7 seconds to go from flight idle to full power.
In initial 747-100 sim training, we did the same thing. The result was a loss of less than 100 feet, the difference being that engine response was almost immediate, and we also could pitch up immediately without noticeable loss of airspeed.
As I remember being told, the big difference in engine response was because the idle position still had a relatively spooled up engine.
The engines running at that relatively high power output even at idle had the drawback that while taxiing the aircraft would accelerate to a higher than permitted taxi speed, which then required braking.

Great answer! Can you explain in more detail why the 747 was more responsive? Was it that flight idle was simply at a higher rpm?

I assume you mean 150 feet instead of 1500 feet.

When going from idle to full power on the 727 was there a risk of surging? (I'm assuming 727 did not have fadec) If so, how did you prevent it?

@DeltaLima I actually meant 1500, and try as I might in rethinking what I wrote, that's the figure that sticks in my mind. Now, given the fact that it's been 26 years since I flew the 727 and that at age 77 dementia is probably setting in, I could be incorrect. I am, however, totally confident in saying that it was hundreds of feet, and I have edited my answer accordingly. Given a descent rate in excess of 2000 fpm and no meaningful power until the last part of the spool up, the point of the demonstration was that you didn't want to get into this condition anywhere close to the ground.

@RoboKaren Perhaps a better way to say it would be that flight idle was a greater percentage of the rpm range on the 747 than it was on the 727, but I'm really not an engineer. Also, I think the engine bypass ratio was higher on the 747. Also, I think the different wing had a lot to do with it. That, plus the 727 would develop a higher sink rate. With the 727 you could come down and slow down at the same time. With the 747 you could come down or slow down, but not at the same time.

@TomMcW No FADEC on the 727-100 or the 747-100/200. I know that when the 727 first flew, there was an engine surge problem, but I never experienced such. Perhaps that was because we were taught to advance the power levers slowly, and never to slam them forward. My guess now is that we typically took around 3 seconds to move the thrust lever from the idle position to the max thrust position.

Your comments triggered me to do some research into the 727. Even at 2000ft per minute in landing config, 1500 feet descent while spooling up is still at least 45 seconds. That is too long for flight idle. What I found is that the 727-200 had excessive drag at flaps 40, and combined with the slow spool of the engines this led to several accidents. For that reason some airlines had a 1500ft stabilised approach criterion for the 727 fleet, others prohibited the use of flaps 40.

@DeltaLima The airline I was flying for had a policy of normal landings at 30 degrees flaps. They allowed 40 for short field operations, and the sim demonstration was done, as I remember, at that setting.

There is not much a jet engine could control.
There is no gearbox in a classical turbofan (not counting accessories such as generators). And those that have it (both future and present, and also turboprops) certainly don't have variable ratio: they barely cope with a single-stage box.
Stator blades do have adjustable pitch on many engines, but it is controlled according to the calculated flow velocity so that their angle was optimal for the conditions. It can't be used to help with rotor speed, or not much.
I'm not aware of any variable pitch rotors on turbojets/turbofans, except perhaps NK-93, which is almost a turboprop.
However, turboprops (and any prop engines) do (or can) use variable prop pitch for better response. Setting 'fine' pitch and thus higher RPM (for the same thrust) allows for faster response than the 'coarse' pitch setting. This is due to two factors: first, the prop is less 'loaded', and second, engine (particularly turbine) response is quicker near max RPM than near idle.
Supersonic engines on military aircraft can also use variable nozzle, but I'm not sure if dynamic response is intentionally included in their operating algorithm. Typically, the nozzle opens near idle, but this is rather for flow stability, esp. during start, than for RPM response.
So, fuel flow remains the main factor of thrust/RPM control. However, on all but the very first generation of turbojets, the pilot doesn't control the 'throttle' directly. (There is no 'throttle' as such). The thrust lever is just a signal to the engine controller, and the controller may modulate the fuel flow in a complex manner. Modern engines 'overcharge' the engine during spool-up, possibly injecting more fuel than in proportion to the lever, and even allowing higher peak temperature than normally allowed, all while controlling stability of the engine.


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Was smoking banned because of passenger safety or occupational safety?
Federal regulation CFR 252.3 notes that:

Air carriers shall prohibit smoking on all scheduled passenger
  flights.

Was this because of: 1) passenger safety concerns (the airplane may catch on fire from an unextinguished cigarette); 2) consumer demand (passengers demanded all-non-smoking flights); or, 3) for occupational safety concerns (the flight attendants were breathing in cigarette smoke all day)?
I've posted my own answer but am happy to be proven incorrect.

Related questions:
• When did inflight smoking become (widely) prohibited?
• Is it legal to smoke in your own plane?

Though I'm not privy to FAA decision-making, I suggest it was really neither of those reasons.  Instead, it was because society had gotten to the point where the non-smoking majority was no longer willing to put up with abuse from the smoking minority.

Perhaps there was more than one single reason.

Related: Is it legal to smoke in your own plane?

@jamesqf Not to mention that cigarette effluent is both poisonous and carcinogenic, as well as foul smelling.

@MarkyMark and the nicotine stains and burn marks left all over the interior are a major PITA to get rid of.

If you look at the part of the Federal code (49 U.S. Code § 41706) that actually instantiates this :

(a) Smoking Prohibition in Interstate and Intrastate Air
  Transportation.— An individual may not smoke— (1) in an aircraft in
  scheduled passenger interstate or intrastate air transportation; or
  (2) in an aircraft in nonscheduled passenger interstate or intrastate
  air transportation, if a flight attendant is a required crewmember on
  the aircraft (as determined by the Administrator of the Federal
  Aviation Administration). (b) Smoking Prohibition in Foreign Air
  Transportation.— The Secretary of Transportation shall require all air
  carriers and foreign air carriers to prohibit smoking— (1) in an
  aircraft in scheduled passenger foreign air transportation; and (2) in
  an aircraft in nonscheduled passenger foreign air transportation, if a
  flight attendant is a required crewmember on the aircraft (as
  determined by the Administrator or a foreign government).

It is the presence of a flight attendant that triggers the non-smoking requirement. Thus, one can safely assume that it is an occupational safety concern (sidestream smoke) that forced the regulation change.

Is a flight attendant required on all scheduled flights, then? Otherwise, the ban on scheduled flights doesn't mention flight attendants.

Good point. I think so but have no hard evidence...  Even the tiniest puddle-jumpers that I've been on have had one attendant. She would close the door, do the pre-flight briefing, sit for the entire trip, then open the door and wave us goodbye.

in fact, is it perfectly OK to smoke on your own small private plane?  so, a plane with no flight attendant?  for that matter, for rich people with their own plane - with pilot(s), but, no flight attendants - is it perfectly ok to smoke in the plane?

@JoeBlow, yes, it is totally legal.

You know, this is probably the most-knowledgeable and generally best site on the network!  :O  thanks!

Interesting. I always thought it came in after the Air Canada 797 accident, but looking into it now I can't say so with certainty. Re the question on flight attendants - FAs are only required on aircraft with more than 19 seats. I worked for a company that operated 18 seat Metroliners with no FAs so the pilot did the safety briefing - no food or drink served however!

If a flight attendant is required from 19+ passengers there could be smoking flights with attendants if there are maximal 19 people on the flight, since the law states "if a flight attendant is a required crewmember on the aircraft". So, if I read this correctly, under 19 ppl you can have smoking flights with attendants!

hi Doge -- yes that would dramatically affect the situation with private aircraft.  I guess you are not REQUIRED to have attendants on large private aircraft (although, I'd imagine many wealthy owners do).  In fact, in that situation maybe smoking is permitted?

@Doge - almost. They're not required on a per passenger basis, they are required on a per seat basis (in some countries it is per doors and not per seats). And if an aircraft has a no smoking sign then that is law, so don't insist upon smoking on any flight!

@Ben And I thought about VArig Flight 820 at Orly - http://en.wikipedia.org/wiki/Varig_Flight_820 - about 10 years before.

I suspect the rules and motivations will vary from country to country. Starting with the rules, for example, ANR 25 (1) specifies that:
 A person shall not smoke anywhere in a prescribed aircraft.

While ANR 25 (6) specifies that:
prescribed aircraft means an aircraft that:
  (a) is a regular public transport aircraft, or an open‑use charter aircraft; and
  (b) is engaged in:
    (i) the carriage of passengers between airports in Australian territory; or
    (ii) Australian international carriage (except the carriage of freight only)

That effectively criminalises smoking on scheduled domestic and international flights as well as charter flights.
In addition, CAR 255 states:
 (1) Subject to subregulation (1A), a person must not smoke:
   (a) in a part of an aircraft in which a notice is permanently displayed indicating that smoking is prohibited at all times or without specifying a period during which smoking is prohibited;
   (b) anywhere in an aircraft during take-off, landing or refuelling or during a period:
     (i) in which a notice is temporarily displayed indicating that smoking is prohibited; or
     (ii) which is specified in a permanently displayed notice as a period during which smoking is prohibited;

Which effectively criminalises smoking on any aircraft where any kind of no smoking sign has been placed.
The reasons stated for the smoking ban vary (and are not usually stated in the laws or regulations themselves), but generally include (1) safety of air crew and passengers, (2) cost savings for airlines and (3) eliminating conflict between smoking and non-smoking passengers.

According to this letter to the House Subcommittee, the flight attendants were seeking for the same protections in their workplace as every other worker. This case study discusses how organized labor negotiated for the change in regulation.

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Why are rotary wing aircraft less efficient than fixed wing aircraft?
This question showed that rotary wing is less efficient than fixed wing, but the answers don't really address why.
Why are rotary wing aircraft less efficient than their fixed-wing counterparts?
It seems to me that the most important thing for efficiency is lift-to-drag ratio, so what makes this ratio much worse in rotary wing? Presumably it can use the same airfoil shape as fixed wing aircraft, so I could imagine a similar lift to drag ratio.

Presumably it can use the same airfoil shape as fixed wing aircraft  No, your "presumably" is incorrect.  The answers below identify a few reasons why.

Quick answer:

The rotary wing is moving at different speeds over the radius, and on the left and right side in forward flight, and since there can be only one optimum speed, most of the rotor is working at less than optimum speeds, lowering the lift-to-drag ratio overall.
The slim rotor blade needs a reflex airfoil, an airfoil with low pitching moment, which is less efficient at creating high lift coefficients. If it would use a regular wing airfoil, it would twist horribly.

Nice concise answer. The only thing I would add is that the speed is not only different over the radius, but also differs between the forward moving blade and the backward moving blade when the helicopter has forward speed. The tip of the forward moving blade can be get close to Mach 1, while the tip of the backward going blade is at Mach 0.6. The inner section of the backward going blade can experience reverse airflow.

@Delta Lima: Correct and very valid comment. I modified the answer to include this aspect.

Setting aside the difficulties of actually achieving such a thing, could efficiency be improved by having separate pitch control swash plates for the inner and outer edges of the rotor?

@supercat: Yes, any way to locally improve efficiency would help. You could even segment the blade and make the segments change pitch independently, for example by an actively controlled flap at the trailing edge.

Very good question. Lower efficiency is exactly the same thing as lower lift-to-drag ratio.
Helicopters have a lot of extra drag that fixed wing planes don't have:

Complex interference drag from the rotor/fuselage etc. interaction.
In forward flight: higher induced drag, due to the disk shaped lifting surface having a much lower aspect ratio than fixed wings.
Part of this disk being pretty ineffective: the inner bit, around the swash plate, has very low linear velocity and does not effectively contribute to the lift, but does to the drag.
The two factors named by @Peter Kämpf play a role.
The tail rotor burning fuel mentioned by @Simon at another question does not help fuel efficiency either.

The rotor having to generate forward thrust as well as vertical thrust is not that much a factor per se. Tilt the rotor 10 deg forward and the lift only reduces by cos 10 = 1.5%, while generating forward thrust of sin 10 = 17%

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Why was the Spitfire's elliptical wing almost uncopied by other aircraft of World War 2?
The Spitfire was one of the most successful designs of its day, with flying qualities of a similar standard to the other best designs of the era. In its decade of production from 1936 it grew bigger, stronger and faster.
Yet there seems to be almost no appetite from any of the major aircraft-manufacturing powers to emulate its most iconic feature. In fact, there is only one mass-produced aircraft of that time with an elliptical wing, the American P-47 Thunderbolt. Nothing German or Japanese, and nothing more from the British either.
In a period where every manufacturer was trying to gain every last bit of advantage, it seems odd that a prime design feature attracted so little appetite to copy.
There are good explanations here on the aerodynamics or performance of the elliptical wing. Why is it so rare when it demonstrably works so well?

Source

Note that even Spitfires were manufactured in "clipped wing" variants during the war which had the wingtips squared off. This was to improve the low altitude speed and roll rate, which is an important factor in air combat but not so much in other types of aviation.

Note that the your link about performance contains in the accepted answer: " Both weight and stall characteristics of elliptical wings are less than optimum; the low induced drag coefficient is bought with higher structural mass and, consequently, lift."

Interesting article on Air & Space.

Interestingly, I couldn't find an answer to this question on the website, but I've found an answer of Peter Kämpf on Quora. He brings forth the same arguments I wanted to mention, so I'll repeat them here.
Elliptical wings are very good - aerodynamically. If you want to minimize induced drag for a given lift requirement, you end up with an elliptical wing.
But a plane is not only aerodynamics.
You also have to consider:

Weight, an elliptical wing is not structurally efficient, and will lead to a higher weight, which leads to higher lift requirements which will lead to more induced drag, even with a very efficient wing.
Controllability, where and how the wing stalls determines if you're able to recover from a stall. Elliptical wings stall tip first, leading to bad stall behavior.
Manufacturability, a fully elliptical wing is very hard to make, with its double curves. This will make the wing more expensive.

If you include these factors, you'll see that you'll end up with a compromise. If you use wing taper (which is somewhat close to the aerodynamic optimal shape) but much easier to make and much lighter you'll see that you'll end up with a better design overall.
An analysis of how the design of a wing changes if you include the structural requirements was done by Jones and can be found here.

I wonder if they ever tried the Spitfire wing with the curved shape forward and a straight back, almost like a half ellipse. May have been a little faster.

The real killer was having to make compound stamping dies for the LE wing skins.  The P-47 got a lot of the way there by making just the TE eliptical, allowing just straight bent leading edges.  Overall, the Spit, like the Merlin had the typically British characteristic of very high parts count, of components being made from 5 pieces where an American aircraft would make them from one or two. Fuselage formers made from numerous little bits, etc.

"Elliptical wings are very good - aerodynamically. If you want to minimize induced drag for a given lift requirement, you end up with an elliptical wing."
That is incorrect.

@Lysistrata, can you elaborate? This answer seems to agree with me

If you go tons faster, you minimize induced drag.  Few people comprehend 300 mph wind force, and they were already on their way to 400 mph.  The thinking behind this type of wing simply was superseded by newer design requirements focused on the leading edge and compressability.  They did get one thing right though, they made it thin, and the Spitfire line lasted until the 1950s.

Should "recover from a wing" perhaps have been "... from a spin"?

If I recall correctly, some years back I read that Spitfire wings stall even worse than tip-first. They stall all at once leading to very sudden and abrupt stalls.

@RoiMaison. It is regurgitating the old myth that elliptical planforms produce elliptical pressure distributions. They don't. And I wish people would stop propagating that nonsense.

@HenningMakholm, it should have been stall, edited it, thanks!

@Lysistrata, with elaborate I meant something more than "it's a myth".I'm interested in your points, but I think this is not the best place for such a discussion. If you could post an answer in the question I linked to, we can further discuss it over there.

@ROIMaison: My reasons are given (with citations) in the comments on the very question you referred to yourself.

@Lysistrata, I also saw that, thanks, I'll have a look into it.

Well the short answer is the elliptical wing was used on a lot more aircraft than this article lets on.
The following all used an elliptical wing and there are others too:

German Heinkel 112 fighter
German Heinkel 111 bomber
German Heinkel 70
US P35
US P43
Italian Reggiane 2000
Japanese Aichi D3A "Val" dive bomber
British Hawker Tempest

I've never heard of any of those. And I doubt I'd have ever heard of a Spitfire if it didn't have "its most iconic feature" inside it, the Rolls-Royce Merlin

@Mazura He 111 and Tempest are very well known aircraft. He 111  was the main German bomber nd an important target of Spitfires. And although RR Merlin is well known too, it is hardly the reason to know Spitfire unless you are an aviation engines geek (i.e. Lancasters and Mosquitos would have to be much more famous than they are.).

Thanks but I suggest that's quite a broad definition of both elliptical and mass-produced.

I wouldn't describe the P43 as elliptical wing

@PartyArk How do you define elliptical that you find the answer uses a broad definition?

Fair question - Well of your examples I'd suggest only the Heinkels and the Val have truly elliptical wings; the rest have straight or almost straight leading edges. However, the 111 and 70 pre-date the Spitfire and are a completely different class of aircraft so don't really qualify per the question  (also the 111 reverted to straight edges); while the 112 was never mass produced. I didnt know about the Val - that's a good example of a mass-produced WW2 elliptical wing aircraft of broadly the same type as Spitfire.

Short answer: Elliptical wings are too expensive to manufacture. A trapezoid wing with a defined geometric or aerodynamic twist can get very close to an elliptical lift distribution (optimal lift distribution over the wingspan, therefore the primary goal of the wing design).

Welcome to Aviation.SE!  Adding some sources by editing your answer would really improve your answer.

Just like houses that aren't made out of rectangles;  harder to make, and thus more expensive.

A lot of planes still use elliptical wings - sort of.
What the maths tell us is that the most efficient wing configuration for a given wing span should have an elliptical lift distribution*. The most obvious way to implement this is to make your wings elliptical.
But aircraft designers learned from the experience of manufacturing the Spitfire that elliptical wings are more difficult to manufacture leading to increased cost and manufacturing time.
So later in the war when resources became tight and everyone assumed that they were racing the Germans to build better, faster planes designers deliberately chose to use straight wings to ease production and reduce costs. The P51 Mustang was designed this way.
But we have learned that making your wing elliptical isn't the only way to have elliptical lift distribution. To get elliptical lift distribution you can:

Make your wing more elliptical
Add washout to tune lift distribution along the wing
Change airfoil profile from root to tip to change lift distribution
Do any combination of the above (eg. washout + rounded tips)

So a lot of planes still use elliptical wings. Especially when fuel economy is one of the main driving design objective. It's just that they don't look elliptical.

* note: There is evidence that this may not be accurate. It is true that if you fix your wingspan the maths will output an elliptical distribution but if you fix your weight (ie. lift at cruise) the most efficient distribution turns out to be something else (something bell shaped) but you end up needing to extend your wingspan

This is too imprecise to be useful. What maths are you talking about? Do you have any citations (from reputable sources) to back up your statements?

@Lysistrata THE standard maths when calculating lift distribution: Prandtl's lifting line theory (google "lifting line theory")

Thanks. Lifting line theory is particularly inaccurate near the wing tips. It is a very poor choice for wings with aspect ratios as small as those of the Spitfire.

In the USA we say "math" not "maths" : ;

It had nothing to do with maneuverability, and it had nothing to do with the added cost of manufacturability. Those were incidental attributes.
The Spitfire had elliptical wings because it allowed for a greater platform to accommodate the machine guns, landing gear, hydraulics and such. It was the same logic for the P-47 Thunderbolt.
It is true that elliptical wings were a bit more expensive and more awkward to produce, yet not by that much. If they were necessary, they would have been adopted without issue. They became increasingly unnecessary as very rapidly, the nature of air power experienced huge change through the 1950s and 60s. There was no longer a need for dogfighters, and more need for jets to be radar and missile-firing platforms.
The performance and operational needs of jet aircraft have many more efficient possible designs than elliptical designs. That's why elliptical designs aren't used.
There is no manufacturing or cost issue that would prevent elliptical designs being used by air forces around the world, if they were truthfully the most effective.
EDIT: Also, if we're being perfectly technical here as some seem to require, the Spitfire doesn't even use a 'true' elliptical wing in the first place because of stability/center of lift issues.

So you are saying that an elliptical wing has never been particularly attractive as far as aerodynamic efficiency is concerned, it was just chosen to maximize internal volume?    And you are also saying that the trend away from dogfighting (maneuvering) helped to reduce the attractiveness (from a designer's viewpoint) of the elliptical wing?

The question isn't why was the elliptical wing used, but why wasn't it used in other aircraft. This post doesn't answer that question, and is a comment (critique) on another answer.

@RalphJ -- actually I'd say last half of third paragraph and all of fourth paragraph attempt to address why elliptical wings aren't used more.  It's just that since we already know that everything in aviation is a trade-off anyway, saying "because it isn't necessary" isn't helpful.  We know there are some advantages, so what are the dis-advantages?  Apparently nothing to do with" manufacturing complexities, according to this answer-- so what rhen??

I addressed the question as well as it could be addressed: If it were a significant increase to any platform's efficiency or lethality, elliptical wings would be utilized. It's a myth that its original intent was for maneuverability. It was for accommodating the machine guns and landing gear. Later generations of warfighting platforms used different technology and were motivated by different operational needs and philosophies. Jet fighters quickly evolved to utilize the most efficient and effective wing design for their mission and payloads. Cost/production has nothing to do with it.

The main drawback of the Spitfire's elliptical wing was the the amount of labour required to build it. Overall the Spitfire required about five times as many man-hours to build as the nearest German equivalent, the Messerschmitt Bf 109.

That's very interesting - do you have a source for the 5x man-hours?

Corelli Barnett, in Audit of War, ruefully compares the 13,000 man-hours needed to make a Spitfire Mk V airframe with the 4,000 for an Me 109G. (The Spitfire also took two-and-a-half times as long to make as a Hurricane, though Barnett does not mention this.)

13,000 man hours for the Spitfire compared with 4000 for the Bf 109 would be 3.25 times as many man hours, but the actual figures would have varied during the period of several years in which both aircraft were in production.

One internet source quotes figures of 15,200 man hours for the Spitfire, 10,000 for the Hurricane and 6000 for the Bf 109 in early 1940, also a variable figure of between 2000 and 10000 man hours for the different models of the Bf 109.

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text:
Single Engine Rating
I am CPL(A) holder with MEP(land) and IR rating. I need to make extra hours to build up my hours on my logbook. However, I was thinking if this would be possible on a single engine without having a SEP rating? Is it possible to fly SE with a flight instructor as an education flight or so and not having the SEP rating or do I have to get a SEP rating?

ICAO licensed countries. Middle east and Asia region. I asked to many schools and each time I get a different answer. Some say you can fly dual with a flight instructor and some say that is absolutely not allowed without having the rating, because that will only give you a flight experience without the hours counting.

If you are MEP rated, the SEP rating should be quite simple of an endeavor.  I would just go and get it.

You can't just say "ICAO licensed countries" because every country has slightly different rules. For example that I'm familiar with, Australia and New Zealand are two very similar countries, yet NZ doesn't even have a concept of a SEP rating (every aircraft is type-rated there).

Wbeard52 thank you for your answer and motivation. I guess I will just get it indeed.
@Ben thank you for your answer as well. My apologies, I will be more specific. I asked some schools and countries like Egypt, Indonesia and India. For myself Im based in Indonesia and each school and flight instructor tells me a different answer.

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What are the bumps in the F-22 Raptor wing for?

As you can see in the picture there are several bulges or bumps in the wing that are located in the aileron and flaps. Somebody told me these are to hide the linear actuator, pushrod, and control horn. However, if the bulge is connected to the wing and aileron how is it possible for it to be there? If the aileron is moving independent of the wing, how is the bulge connected to both at the same time?

Contrail storage canisters

Yes they are fairings for the actuating mechanism for the control surface.  I can't speak directly to the F-22's details but, this kind of thing is done on lots of airplanes.  The F-22's control surface blister fairings are perhaps a bit more sophisticated and 100 times more expensive, but the concept isn't all that special.
The blister on the fixed structure will have an overlap with the blister on the moving element.  The blister on the moving element, like the aileron in the image below, will slip under the fixed part of the blister when it moves down, and there will be additional material forward of the joint that is exposed when the aileron moves up to maintain the contour.
In the somewhat grainy image, you can make out a dark line along the interface between aileron and wing that follows the profile of the blister (along with staining that could be discoloration from seeping hydraulic fluid).  There is likely a flexible seal strip to provide the smoothest possible transition but with enough compliance to accommodate the geometric changes in the surface contour, as the two halves of the bulge telescope with each other, and still keep the aerodynamic seal.

In profile it would look something like this:

I still dont understand. Could you please post a video?

What don’t you understand?  Please be specific about what is unclear to you.  Half the bulge is part of the wing, and half is part of the aileron.  They are formed to allow them to move independently as John depicted  in his excellent sketch.  Unless there is an F22 mech here who can go take one apart for some photos that’s probably about as good of an answer as you’re going to get here...

@MichaelHall Also, I'm guessing than F-22 mech taking this apart, making a video of how it works, and then posting said video on the Internet would likely face a court martial very quickly.

@LukeJustin The blisters are indeed aerodynamic fairings to cover the actuators for the trailing edge surfaces. The blisters consist of two pieces each, not one. The forward half of them is part of the wing, while the aft half of them is part of the movable surface. As the answer points out, you can see the seem line between these two pieces on each of the blisters in your photo.

@reirab so what you are saying is that each half is connected via some sort of hinge so it allows it to move?

@LukeJustin More or less, yes. The two halves can rotate relative to each other. The mechanisms that connect the movable surface to the wing and which control the deflection of the movable surface are inside the blister. The blister is just an aerodynamic housing around them.

Ok..btw the video i meat a video of the aielron moving so i could see how the blisters move and how the look when im motion...i could find any videos like that

@LukeJustin I added some annotations to my sketch to help.  The blister on the aileron will be shaped to allow the overall contour to be maintained as the blister moves on the aileron hinge arc of motion.  Basically an arc shaped telescoping effect.

@LukeJustin, what JohnK is describing can be thought about generically like this. Think about the overlapping segments of a medieval Knight's armor. In order for the arm, shoulder, torso and/or legs to have movement and still provide protections, the armor segments are designed to overlap and move over one another to the extent of the design allows. A snakes scales would be another example of this idea in a nature.

@JustinA that's not bad.

@LukeJustin - your question is interesting, but , it's almost impossible you could find such a detailed video that literally shows the detailed workings of such a classified aircraft! It's just some sort of hinge that cleverly maintains as small a gap as possible. You won't be able to get any more detailed info than that. Thanks for the cool question. Don't forget to tick an answer please.

Ok thanks. I just want to a video of like a preflight check where they move the aielrons. However in all those videos its a striahgt  on view so you can really see the aielrons moving. That all I wanted to see. I wanted to see how the blisters moved when the aielrons moved. A detailed dirgam would help but I really need to see a visual irl

@reriab this is what i meant above

https://www.youtube.com/watch?v=jSWgXz994XE shows the rudder move, with a view of a similar fairing.

Conceptually, it is a ball and socket.
Practically, it is a cross-section of a ball and socket joint. It does not have a hinge.
The defined shape of the bulge is not set by its own motion at all and is shaped in the way that it is so that it will maintain its general shape at all possible positions along its plane of motion. I would assume the value is to the aerodynamic calculations and not having to constantly account for drastically different surface area and shape depending on if the plane if flying up or down;keeping values as static as possible. The drawing is pretty accurate in the way it shows what you are talking about, is essentially, a hinge 'cover'.


text:
Do "Civil Aviation Regulations" and "Aeronautics Bulletins" still have any legal authority today?
This is a history of the FAA from their site.
In the U.S., we had the original set of aviation laws known as aeronautical bulletins back in the 1920's and 1930's. Later (in 1938) we had the Civil Aviation Regulations (CARs), created by the Civil Aeronautics Authority (CAA), added to them.
I am curious if those laws were actually repealed or simply made redundant by today's regulations and whether or not there were additional laws not seen in the FARs today but which did exist in the CARs and Aeronautical Bulletins.

Many aircraft were certified to CAR standards.  Those aircraft still have to meet those standard.  Even a brand new aircraft off the line today, that is produced  based on a type certificate data sheet that has CAR regulations has to meet those regulations.

Great addition!  I didn't think about that.

Where is the source of this rule?  I searched a little bit, but I'm not finding it.

Take a look at a type certificate data sheet, and it includes the certification basis in it.  Typically there are multiple basis with specific regulations called out.  For example the 727 is a CAR 4b aircraft, with a few exemptions http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/5d48fc77a31b7f6985256722006b0c1c/$FILE/A3we.pdf

No, except for a type certification rule.

Aug 23, 1958:
President Eisenhower signed the Federal Aviation Act of 1958 (P.L.
  85-726) into law. Treating comprehensively the Federal role in
  fostering and regulating civil aeronautics and air commerce, the new
  statute repealed the Air Commerce Act of 1926, the Civil Aeronautics
  Act of 1938, the Airways Modernization Act of 1957, and those portions
  of the various Presidential reorganization plans dealing with civil
  aviation.

The aviation law slate was wiped clean and started fresh with the FAA, although many of the principles in the aeronautical bulletins and the Civil Aviation Regulations were clearly incorporated into the FARs we know today.

In a way it's a yes, if you see an old bulletin there's a good chance it means there a reg somewhere.

authors: Олександр Григор'єв


text:
Medical - Must use corrective lens(es)…
Recently went to Flight Safety for the first time and one of the instructors was talking about the time he got ramp-checked and they asked him after looking at his medical if he had his two pairs of glasses on board. I can’t find a regulation anywhere that requires you to have two different sets. Is that a company requirement normally or am I missing the regulation somewhere?
I normally wear contacts with a backup pair of glasses and want to make sure I am legal in my 135. Not seeing anything in the GOM or Ops that would require anything beyond the FAA and ICAO requirement.

For domestic flights, it's recommended but not required. For oceanic or international flights it's required under ICAO rules. The FAA published an InFO document on the topic here.
The ICAO requirements are in Annex 1:

Where this standard of visual acuity can be obtained
only with correcting lenses, the applicant may be assessed as fit provided that:
a) such correcting lenses are worn during the exercise of the privileges of the licence or rating applied for or held; and
b) in addition, a pair of suitable correcting spectacles is kept readily available during the exercise of the privileges of the
applicant’s licence.

So you need to be wearing a set of lenses (i.e. contacts are fine) and have a spare pair of spectacles (i.e. contacts are not fine for the spare). One pair of contacts and one pair of eyeglasses are fine as long as you're wearing the contacts.

Correct, I saw that as well but didn’t know if that meant that I was required to bring my contacts and two sets of glasses or just the contacts and the glasses I normally bring as well. My understanding would be that I am good with contacts and one set of spare lenses but don't want to be caught out. Appreciate the help.

@JonathanWilkinson Contacts and spare glasses are fine per ICAO. You should of course make sure the country you're flying in doesn't have stricter laws.

And, of course, always have at least one spare set of contacts just in case you loose/tear one. Sure, you may finish this flight with the glasses, but you wear contacts because (most likely) you prefer them.


text:
How can the Perlan II glider climb to 90,000 feet?
I've been reading material about the Perlan II experimental glider. They hope to take it up to 90,000 feet  -- higher even than an SR-71 BlackBird.
But the Perlan II is just a glider. Can it really just climb thermals up to that level? Is there something special about its aerodynamic design that lets it do that -- or are all gliders capable of climbing as high as possible, with only the  heat and oxygen needs of the human occupants being the limiting factor? Or is it just me that finds it odd that a glider can climb higher than  a powered aircraft?

Perlan II will climb to extreme altitudes on wave lift, not thermal lift. Wave lift is created when strong winds blow approximately perpendicular to a mountain range, and the wind speed increases steadily with altitude. This creates a standing wave in the atmosphere, kind of like the ripple behind a rock in a fast moving stream of water. On the leading edge of the wave, air is moving up, and that's where gliders fly. Standing waves can reach very high into the atomosphere, which is why Perlan II is expected to reach 90,000 feet.
Perlan II is different from normal gliders in that its wing is optimized for minimum sink, instead of best glide ratio. It's meant to float along while losing a minimum of altitude, which makes sense if it's going to fly in nothing but wave. Normal gliders are usually optimized more for gliding long distances, for which glide ratio is more important than minimum sink. Interestingly, Perlan II's wing looks a lot like RC model glider wings, which are also optimized for minimum sink, since RC gliders don't typically fly cross country.

Welcome to StackExchange and thanks for such a great first answer! Could you please explain for the truly ignorant (such as myself) what the difference between "minimum sink" and "best glide ratio" -- either with links or in-text? Thanks!

@RoboKaren: min-sink and glide ratio are standard terms in aerodynamics. Sink rate is how much altitude you lose over time, for example, how many feet per second. So minimum sink is the lowest sink rate you can get. Glide ratio is how much distance you can travel per given loss of altitude, for example, how many feet per feet. So max glide ratio is the shallowest angle you can glide at.

See my answer on minimum sink versus best glide http://aviation.stackexchange.com/a/25496/9195


text:
Would a flight of F-35s from Texas to Denmark have their transponders searchable on e.g. flightradar24.com?
Lockheed Martin is delivering four F-35s to Denmark today. With a stop at the Azores and ETA 14:00 CET.
Would I be able to find them on a public site like Flight Radar? I see a tail number of L-010 on one news article, but that did not result in anything useful...

A 12-minute clip (in Danish).

@PeterMortensen indeed. There was a lot of coverage. but it would have been interesting to follow it. I hope you saw the flyover with an F35 and some F16s a few weeks back.

It's not always possible to search for military planes by tail number on Flightradar24, and you just have to look for them. And as mentioned in another answer, you might have a better chance of them appearing in ADS-B Exchange, because Flightradar24 seems to do more filtering on military aircraft.
Also ADS-B Exchange has an option to display military only (by pressing "U") which makes it easier to locate them, especially in crowded airspaces.

It is unlikely that the F-35s transmit ADS-B data, so Flight Radar 24 can only track them if the aircraft are in range of a number of ground stations so that multilateration is possible. This means that over the ocean, tracking will not be possible.
As far as I know, Flight Radar 24 suppresses military flight data on request, so it could well be that the flights don't show up, even if they technically can be tracked.
Other websites, such as ADSBExchange, may do less filtering.

I was seeing a lot of military jets around the UK, and a US stratotanker in the North Sea, which led me to conclude that it may have been a possibility

Can WAM work without ADS-B broadcast?

@mins Yes. WAM can work on any signal that can be accurately timed. For aircraft surveillance, any messages on the 1090 MHz frequency can be used, but especially Mode S message are very easy to work with because the contain identity information (24 bit address). Mode A/C messages are substantially more difficult to multilaterate, because multiple aircraft may sent out the exact same message which make correlating the messages from the same aircraft at various receivers difficult.

I didn't realize that WAM is so extensively used now. I learned quite a bit from your answer on the multilateration question.


text:
Can pilots smoke in the cockpit of an airliner?
An answer on travel.se suggests that some pilots are smoking on long-distance passenger flights.
Can passenger airliner pilots smoke if both the captain and first officer agree it’s ok? If I recall, smoking is only prohibited on flights that require cabin crew as a crew health issue (sidestream smoke) and not as flight safety issue. Given that cabin crew are not on the flight deck, is there anything that prevents a pilot on a larger airline from lighting up?
For the purposes of the question, let’s consider flights originating in  USA, EU, UAE, and China as the four biggest country/areas.

What country/airline?

Thanks. Good point. The originating anecdote wasn’t clear. I’m sure the USA and EU wouldn’t permit it but maybe flights out of UAE or China might. Added to question.

According to the BBC "Chinese flight regulations prohibit all flight crew from smoking, and banned passengers from using e-cigarettes on board in 2006."

All of the most significant countries prohibit smoking on airline flights, either through national, industry, or airline regulations. This applies to crew through different regulations, but as strictly as to the passengers.
Pilots can and sometimes do smoke in the cockpits of business jets. These can be as large as airliners (see BBJ), but usually aren't.

Even when a country and/or airline ban smoking in the flight  deck, some pilots will ignore the ban and still light up.  This was quite common with Asian carriers in the past. I am not sure how often it happens today.

Mike - you are very correct. On a flight from LA to China recently you could absolutely smell cigarette smoke in the first class cabin so I asked a flight attendant about it and he said the pilots smoke all the time.


text:
Can the APU provide emergency thrust?
By David Monniaux (Own work) [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.0 fr], via Wikimedia Commons
Many larger airplanes have gas turbine APUs (auxiliary power units). It seems that their exhaust is oriented to the rear and might provide some thrust.
How much thrust does an APU provide and would it be enough to keep flying an airplane if the main engines went out?

Good news: you can maintain flight with just the APU. Bad news: you can only do this until you run out of altitude and airspeed. :) Same is true without the APU (i.e. your airplane is now a glider.)

As an interesting aside, Cessna calculated that it's light airplane reciprocating engine exhaust was producing up to about 5-10lbs thrust so in some later models they began to angle them back instead of straight down.  Not insignificant where every little bit helps. They estimated it would take about 30lbs of thrust to maintain level flight. So, if your prop comes off, firewall the engine and extend your glide! (until the engine flies apart)

The Antonov An-26B cargo aircraft (produced in the Soviet Union) has a Tumansky RU19A-300 combined APU and jet engine mounted on the wing behind the right main engine. This unit provides additional thrust up to 800 kg to improve takeoff and safety in case of engine failure.
This information is from the accident investigation report of Polish aircraft An-26B SP-FDO in Tallinn, Estonia on March 18. 2010. During the flight from Helsinki to Tallinn, 9.5 NM from Tallinn the left engine failed, and the thrust-providing APU could not be started. The aircraft was not configured for landing, flew over the runway and made landing on snow- and ice-covered lake Ülemiste (main supply of drinking water).

This sounds nearly the same as the initial plan for the HS Trident 3B's booster engine, but the APU removal scrapped due to fuel consumption.

"The RU 19-300 was shot down after takeoff. " -- man, that's a pretty bland accident report to hide such a significant event!

" With RU19A-300 operating the critical engine is left engine, with inoperative RU19A-300 the critical engine is right engine." -- fascinating--

The amount of thrust available from an APU would be minuscule as it is designed drive various aircraft systems and adding on a nozzling system geared for propulsion would reduce the power available for doing it's intended work.
Even if an APU was re-purposed for propulsion, it most likely would not be enough to have any significant role. While horsepower and thrust are dissimilar terms that do not have a simple conversion, we can do some comparisons to show how under-powered an APU would be
An Airbus 350 has a pair of jet engines which combine to produce about 195,00 lb-ft of torque.
This same aircraft has an APU which can produce up to 1700 equivalent shaft horsepower.
The Airbus 400 has 4 turboprops that combine to produce 45,000 HP, and has a max takeoff weight roughly 1/2 that of the A300.
While I am in no way an aeronautical engineer; and these comparisons are on the order of apples and oranges, I don't think it is a grasp to say "it ain't happening" to an APU providing propulsion.

Not alone, but APU can help to get more thrust by taking over the duty to supply the bleed air from the main engines.

Practically speaking, APUs are not sufficiently powerful to provide the thrust necessary to maintain level flight. It is an issue of power (as well as having that power effectively converted to thrust).  The APU is designed to provide electrical, bleed air (for environmental control, and for starting other engines), and in some cases they may run other accessories.
It may be possible to have more power available to the main engine(s) if the APU is used for electrical, bleed air, etc.  Normally, this is not done in most aircraft.

Thanks to pots and Federico for their answer mentioning the Tumansky RU 19A-300 combined APU and jet engine.
Further search found a NASA paper from 1968 using a GE TF-34 "convertible" turbine that could unload the generator shaft and redirect the power output with "variable inlet guide vanes" to a turbofan.
Around 8000 lbs of thrust could be created as a turbo fan alone.  Combinations of thrust and shaft power were also possible.
Generally, an engine out/landing emergency will be in a speed range where a turbo fan (or prop) will be effective (around 150 - 250 knots).
So, maybe the tri-jet isn't dead, it just needs to be tweaked a bit.  There are tales of using the 3rd top mounted jet to control pitch-up as well.


text:
USA: Why don't airports raise landing fees to make up for low passenger fees?
A question from travel.stackexchange.com about luggage carts prompted a discussion on the economics of airports. The gist was:
American airports have much lower passenger service fees which
 are capped at USD4.50 per FAA rules than foreign airports, which can easily be USD20-50 per person. This results in much
 lower number of amenities at American airports compared to other international airports.
You’d think they’d try to make it back with landing fees.  But Tokyo Narita airport’s landing fee is JPY1550-2000 yen per tonne. A 787-8 has a weight of 172 t so the fee would be ¥258,000 - ¥344,000 or so or roughly USD2300 - USD3100. San Francisco SFO’s landing fee is USD5.54 per thousand pounds. A 787-8 landing weight is 379,200 pounds so the landing fee is around USD2100. There doesn’t appear to be a significant delta here to account for the difference in passenger fees.
My question is: Why don't airports simply increase the landing fees to compensate for the lower per-passenger fees?

When answering the linked question about luggage carts, I had actually calculated the landing fees for Narita vs. SFO and they were quite comparable. It's only the passenger fees that are much higher on the non-USA side.

FYI, since you use ¥ for the Yen, if you wish to use $ you simply have to put a \  before it to prevent the MathJax interpreter from interfering.

"This results in much lower number of amenities at American airports compared to other international airports." Is there evidence for this? Some US airports have more amenities than others, and we can point to specific small differences (e.g. luggage cart policies), but it's not as though European airports are handing out free champagne to all passengers while US airports have dirt floors and baggage delivered by donkeys.

This depends on where you are in the country and more specifically who controls the airport. A lot of airports in the US are owned by cities (or local governments) in some capacity. As such changing the landing fees often requires a legislative change which is not always easy. For example here is the legislation that covers the landing fees at both major airports Philadelphia Controls

Changing these requires a policy change at the government level and it takes a long time to get just about anything through the Philadelphia government. In many cases these fees are paid to the municipality anyway and the airport never sees any of the money so the fees don't (directly) help the airport. In a lot of cases the fees do (or at least are presumed) to go back to the maintenance and upkeep of the airport.
Private airports (generally smaller GA ones) can levy fees as they see fit and sometimes do to help with the upkeep of the field.
What airports or more specifically FBO's and other on field operators do is raise operational costs to use their facilities. Rising FBO fees have been of concern lately and sometimes there is no way to escape them if someone has what amounts to all the parking space on the field. It may only cost $5 to land somewhere but keeping your plane there for a while, getting a pre-heat, maybe even using a terminal is by no means cheap.

Great answer! Can you explain or link to what an FBO is?

@RoboKaren I have added a link with some info on what an FBO is. Generally speaking its an all encompassing term for the organization's that are based on an airfield and provide common services like fuel, parking, terminals, maintenance etc. At some large international airports the situation is a bit more complex.

Fee setting is complicated. First, it should be noted the $4.50 per flight segment PFC charge is not intended to provide for terminal amenity improvements. As described by the FAA, the stated purpose of the Passenger Facility Charge (PFC) Program is:

Airports use these fees to fund FAA-approved projects that enhance safety, security, or capacity; reduce noise; or increase air carrier competition.

In addition, the structure of how landing fees are imposed varies. This article provides a good overview of how US airports set fees. Airports set the landing fee based on airfield costs. This guidance can also be found directly from the FAA.

h. Airfield Revenue. Unless users agree otherwise, airfield fees generally may not exceed the airfield capital and operating costs of existing airfield facilities and services.

Why don't airport simply raise landing fees? Airports do impose fees, just not through the landing fee mechanism. Looking at the Port of Seattle's Schedule of Fees, we can see the other fees the airport collects from airlines.

I think it's simply because passengers don't want to pay for free carts. Ultimately, all costs are going back to the customer via fares.
It's similar to raising ticket prices and bringing back "free" food or check-ins or extra legroom; certain people in certain situations will go for it, first class or business travel, but the market has shown that most will instead choose the option with lower fares.
Instead of the airport forcing everybody to pay for it, airlines are free to offer it themselves. In fact, airlines will have somebody carry your luggage from your house to check-in, if you buy the right ticket.

Totally unrelated, but I love the fact that at your link it says, "we’ll drive you to and from the airport so you can focus on what drives you", then there's a picture of the passenger gazing vacantly out the window...


text:
Why isn't testing fuel flow from both tanks a run-up checklist item?
On most single engine GA aircraft, testing both mags is always on the checklist. For a plane (like a Mooney M20) that doesn't have a "both" selector, it would seem prudent to throw the switch to verify there is not a flow issue from either tank.
Is there any good reason why not to run this test, or is it just not considered worth the effort?

There is a very good reason not to run this test: If it is not done perfectly your engine can become starved of fuel during takeoff.
For simplicity let's assume your fuel selector only has two positions (Left and Right) and think about what's involved in the test and a few things that can go wrong:
What are we testing?
One of the points of an engine Runup is to verify that the fuel system can deliver a fuel flow sufficient to allow the engine to develop takeoff power. There are other things we're verifying but let's stick with that item for this discussion.
How can we verify this?
We verify that the fuel system has adequate flow by running the engine up to something resembling takeoff power (most runup checklists don't have you go to full throttle, but you advance the throttle enough that the engine is demanding a significant fuel flow compared to idling and taxiing around).
To verify that your fuel system is allowing sufficient fuel flow from each tank you would have to switch tanks during the engine run-up (with the engine at runup power) and wait long enough to exhaust any fuel that might be in the system between the fuel selector and the engine.
If the fuel selector handle comes off in your hand or the engine quits you found the problem on the ground, so you can get a tow back to the ramp and get the fuel system fixed.
What can go wrong?
The test above sounds innocent enough, but it's deceptively dangerous.
Here are two possible failure modes that may make you rethink it:

The second tank doesn't have adequate fuel flow.
This could be a complete obstruction of the tank pickup or just a restriction in one of the lines, but for some reason the second tank will not supply a fuel flow sufficient for takeoff and climb out at full power.
You may miss this if you don't wait long enough at runup power after switching tanks to drain the fuel from the system forward of the fuel selector, and now your engine suddenly got quiet as you're rolling down the runway - or worse it quits 100 feet off the ground and now you're having a Really Bad Day!
You missed the fuel selector detent.
Easy enough to do, especially if fuel selector maintenance has been lacking and the positions are not really distinct (when is the last time you *really, critically, felt the clicks on your plane?). It could happen in the initial switch, or when switching back to the first tank if that's your procedure.
A fuel selector not in a specific tank position may still allow enough fuel flow to complete a runup when combined with the fuel left forward of the fuel selector, but it may be too restricted to allow a takeoff. The fuel selector may also vibrate into an OFF position during takeoff.
In this scenario maybe your engine stops at 200-300 feet, but you're still having a Really Bad Day.

In both of these scenarios the engine is still running because there is fuel in the system between the fuel selector and the engine (the two big reservoirs are the fuel strainer / gascolator & the carburetor float bowl, but there are also fuel lines that will need to drain before the engine dies).
To get an idea how long these reserves last try setting your engine to Runup power and turning off the fuel selector. You may be surprised how long the engine will run before the fuel after the selector is exhausted. Also remember the time will vary based on power setting, mixture setting, and even aircraft attitude sitting on the ground allowing more or less fuel to get to the carburetor from the lines (a nose-high attitude during takeoff may starve your engine more quickly than sitting level on the runup pad).

How can we safely conduct this test?
Making sure your fuel tanks all work is kind of important, especially if you are going to be making a flight near the endurance limit of your fuel.
There is no 100% safe way to conduct this test, but the way I was taught seems to have the fewest possible failure modes:

Start, taxi, Runup, and takeoff should be conducted on one tank.
Typically this is "the fullest tank", but if they're all equally full then either the one the fuel system return flows to if your airplane has such a thing, or just pick one.
By using the one tank for all your ground operations and your Runup you are pretty much guaranteeing that it flows sufficient fuel to allow a takeoff, and that at least this position on the fuel selector works.
After takeoff switch tanks after reaching a safe altitude.
Do this with enough fuel left in the tank you took off on to turn around and get back to where you started in case you discover the tank you switched to doesn't work, and as with any tank switch be prepared for the fuel selector handle to come off in your hand: Know where you'll put the plane if that happens!
If your engine stops a few minutes after you switch tanks…
…you now have a good reason to suspect that the tank you switched to doesn't work.
Per the first rule of troubleshooting, undo the last change you made (switch back to the working tank you took off on) and wait for the engine to get fuel again. When the engine restarts go home: You have a fuel system problem and need to get it fixed.

If after switching back to the working tank your engine doesn't restart…
…make sure you've waited long enough (it doesn't take long, but it FEELS like a long time when the engine is quiet).
If you waited long enough you may have a fuel selector failure. These don't happen often, but they do happen (and this is why you do the test at a safe altitude with a landing spot picked out).
In this unfortunate case run your engine failure checklist and expect to be making that dead-stick landing: Fixing a fuel selector in flight is probably beyond the skills and daring of most pilots.
(Of course you expected this because every time you touch that fuel selector handle you expect it to come off in your hand like I said before, right? Your CFI was like mine and a few minutes after you switched tanks they pulled the throttle on you al the time, so you got this landing made, Right?)

The test process I use and have outlined above is obviously not free of risk, but the risk level is reduced to be the same as any other fuel tank change: You can be reasonably sure that you won't have an engine failure on takeoff when you're close to the ground, trees, people, and other things we try not to hit with our airplanes, and you can pick when you take on the risk of an engine failure to be sure you can safely recover from the situation.

Incidentally there is a way to verify fuel flow from both tanks, at least on the Piper Cherokee: Lock the fuel strainer drain open and let it run until you drain off a good 16+ ounces into a bucket (or go all out and drain a gallon). Pour that back into the tank, flip the fuel selector, and repeat to check the other tank. This also tells you the fuel system is plumbed correctly, because you'll see the level drop in the tank you're draining from. I believe you can do something similar on most GA singles as long as the strainer is after the fuel selector valve..

Awesome answer. Thanks!

Hmm. My checklist has start and taxi on the other tank, and runup and takeoff on the fullest, the rationale being that the run-up will use enough fuel to show that both work.

@falstro I've seen that on some checklists too - I have mixed feelings about it. How safe it is depends on how long your runup is: A "student pilot" runup that takes 30-60 seconds with the instructor explaining each thing you're doing & why would almost certainly drain the system, but a quick "flick the mag switch, hit the carb heat, OK we're good, let's go!" runup might not. Another variation I've seen that's a little saferIMHO is starting on one tank & running on it while you get ATIS/clearances, then switch tanks and do your taxi, runup, and takeoff on the other.

Ok, my run up includes mag-switch, prop governor, carb-heat, vacuum, and idle checks. I'd say it usually takes ~60 seconds. I tend to be meticulous though, and I can see how some might not be. ATIS/clearances on the other hand is exactly 0 seconds at my home field. ;)


text:
At what altitude do vacuum powered gyros become ineffective?
Obviously, in space a vacuum powered gyro would not work because there is no air to move, but, how high do you have to go before they are unable to spin fast enough to work properly?
would a vacuum gyro work properly in a sr71 at 80,000 feet?

"Vacuum" gyro's are differential pressure motors, if you can provide an alternate static source that has a higher pressure than the external static source, the instrument should work fine. Maybe the question should be how much of a pressure differential is needed to run the gyro? I think somewhere around 5psi...

Vacuum powered instruments are typically driven by a pump. I imagine that any installation that will travel to very high altitudes would have one or more pumps that can support the vacuum instruments.


text:
How can citizens assist at an aircraft crash site?
In the event of an accident like that of Yeti Airlines flight 691 in Pokhara, Nepal (where the crash happened outside of the airport), what and how can those who arrive at the crash site first help?
Is there a standard procedure to follow when the medics or security personnel haven’t arrived yet? What’s the danger involved for those who’re assisting?

https://en.wikipedia.org/wiki/Air_France_Flight_358 - you can give people a ride to the hospital if they're hurt, or to the airport if they are not, but need to be mustered

First things first: Immediately upon noticing an accident, report it to officials. Never think "someone else has probably already done that". I've arrived on a traffic accident site three times in my life. In two of those occasions there were already other bystanders there, but all of them were so disoriented that none had called 911.
As for the risks involved, the obvious ones are possible fire / explosions on site, and the collapse of the wreckage. The fire is most likely to ignite upon impact, and planes seldom carry other volatile material than fuel. Secondary explosions are still possible due to pressure vessels, tires etc. I may also be that the crashed plane is a military aircraft, which may carry ammo. On a site like the crash you mentioned, landslides are a possibility also.
Assessing the risks mentioned above may be difficult for a layman, but should one decide to help, I think this is not much different from any other accident type. There is some variation between instructions, but the main steps are:

If there are survivors, assist them. Get the injured safely away from the wreckage if remaining there poses a danger. Give first aid to those in need.
If there is a fire and you have the means, try to suppress it.
When the officials arrive on site, do exactly what they tell you to do.

All in all the main thing is to remain as calm and collected as possible, and do not take unnecessary risks. Doing this will not be easy.
Aside from the above, do not touch anything on the accident site unless it is necessary for saving lives.

Comments are not for extended discussion; this conversation has been moved to chat.

Regarding "get them safely away from the wreckage," I would think this one would come with some caveats. If the plane is on fire, then, yeah, sure, getting everyone out is extremely high priority. If there is no fire or other such immediate risk, though, then moving people without knowing what you're doing may cause more injury than leaving them where they are until professionals arrive. For example, moving someone with a broken bone could cause permanent nerve damage. In the vast majority of commercial airliner accidents, most or all of the injuries come from the evacuation.

@reirab you have a good point, and not that I would doubt that, but care to share some source for the assertion? I slightly edited the A as per your comment.

@Jpe61 The Mayo Clinic's article on first aid for fractures says, "Don't move the person except if necessary to avoid further injury." As far as the nerve part, this is what I was told by every doctor and EMT I encountered when I broke my arm about a year ago. There's a major nerve that runs next to that particular bone, which can be damaged or severed by bone fragments if the fragments move the wrong way. Checking for possible damage to that nerve was one of the first things each of them did.

@Jpe61 Of course, the risk for that particular nerve is something specific to the particular bone that was broken in my case, but it's also exactly the sort of thing that someone without medical training wouldn't know about (I certainly didn't before then.) EMTs and doctors are trained to know what risks moving an injured person may carry, whereas the average person (myself included) wouldn't know and could easily cause more harm than help. In my particular case, damaging that nerve could have permanently disabled my ability to move my wrist and hand on the arm in question.

@Jpe61 It's standard advice for trauma in general--you don't move the patient unless the situation they are in is unsafe.  To the extent possible the emergency crews immobilize any injury potentially involving bones before moving the patient--that stays on until the hospital clears them.

Yea, I know this. Accident sites are, howevwr, ofter chaotic and potentially dangerous.

@reirab "In the vast majority of commercial airliner accidents, most or all of the injuries come from the evacuation." I would like a source for this - I would imagine that most injuries would come from actually crashing into the ground violently at high speeds...

@fgysin The vast majority of commercial airliner accidents (at least in the more developed parts of the world and likely in all of it) do not involve crashing violently into the ground. Incidents that involve evacuation are far more common than ones in which passengers are actually injured prior to evacuation. For example, in the U.S., there has been exactly 1 passenger fatality on mainline U.S.-flagged airlines in the last 20 years. Even when including the small regional airlines, there have been only 2 in the past decade. Accidents that injure passengers directly are exceptionally rare.

@reirab Ok sure, but the question is asking about a crash site. If a minor incident happens during, say, landing then normal citizens are unlikely to just stumble upon it, wondering "gee, I'm the only one around, how could I possibly help?"...

Just to add something to the other very good answers.
I used to be a paramedic and there are two main rules which always apply:

watch out for yourself, always! A dead rescuer doesn't rescue anybody.
if you are not wearing your uniform (i.e. if you are not working as a rescuer) every damage/harm you cause might (depending on the legislation) results in legal action against you. If unsure, just call the most appropriate emergency number and let them guide you because sometimes the best thing to do is simply to assist the person and wait for an ambulance instead of just doing something wrong and not necessary.

That being said, if you are the first one getting on the scene you actually have one of the most important job as a rescuer: collecting information about the accident.
You will be the very first person to alert the appropriate emergency service and giving a good overview of the scene is really important for the emergency system to dispatch the most appropriate rescue service. In particular you should give the exact position of the accident, who has been involved and what has been involved.
Many times happens (it happened also to myself) that upon reaching the scene what you find is very different to what you were alerted for: a bus which had an accident is a very different kind of rescue if it is full of people vs. if only the driver is inside; a motorcyclist who had an accident against a car and is screaming because of a broken leg attracts immediately all the attention... and unfortunately nobody cares about the car driver that had an heart attack and is lying unconscious in the car.
So providing the emergency service with a good overview of the accident (so called triage) is going to be the most important thing to do as first person arriving on the scene.

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I've been thought by european first aids association that you give first aids even if you don't feel competent, because professional help most likely arrives after 6 minutes and people that don't breath will die or be permanently damaged by that time. Also you will not be sued.

"I've been thought by european first aids association " please point to a black on white reference for this statement, otherwise this is plain wrong.
Additionally, part of delivering first aid is also calling for the emergency services.

The legal situation varies greatly from place to place. Some jurisdictions have a duty to rescue under which people must render aid, some have no such duty and expose people to litigation if they render aid and it goes badly, and in between many have good samaritan protections. StackExchange can't give guidance that's going to be correct for every jurisdiction; people need to be aware of what rules apply where they are.

@EarlGrey See cites at https://en.wikipedia.org/wiki/Good_Samaritan_law - it varies country by country, but many European countries have some sort of duty to rescue and accompanying protections for good-faith first-aid.

Re "in legal action": But most jurisdictions have Good Samaritan laws(?) - "The protection is intended to reduce bystanders' hesitation to assist, for fear of being sued or prosecuted for unintentional injury or wrongful death."

Good Samaritan laws is a thing that covers few anglosaxon countries. In general, many countries have a "duty to rescue", which is very different than Good Samaritan law and often simply means that if you see an accident, you should stay there and provide help according to your knowledge and capabilities, which often is simply "ring 911 (or equivalent emergency number). Sometimes no help is the best help, but for sure at least notifying the emergency service is the minimum everyone can do (or ask someone to contact them).

Best way you can assist is by staying out of the way of the professionals.
If you get there before them, help them how you best can by acting as a guide (especially in remote areas) and maybe giving them access to your home or other buildings to set up equipment.
Interfering with their work won't generally be appreciated, obviously.
If you're there before the professionals even know where to go, alert local and regional authorities of where the accident site is located.
Do NOT disturb things, unless you can safely assist any survivors and when so do as little disturbance as possible. Do NOT go souvenir hunting. And keep in mind there will be a lot of dangerous things about (fuel, other chemicals, sharp pieces of metal, etc.). And that the location of any piece may be a clue as to the cause of the accident.

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I'm late to the party, but I think I have some valuable information to add. What I remember from my Polish Red Cross training long time ago is a simple list to use in all mass accident situations:

Your first obligation is to not increase number of casualties, that includes safety of you and other "civilian" respondents. Don't be one more person that needs help, don't let others to be. Paramedics and firefighters will have enough on their plate anyway.

Call emergency line (most likely 112, 911, or 999; see Wikipedia's article on emergency telephone numbers). It's better if everyone do this than if no one does.

Before uniformed responders (paramedics, police, fire department etc) arrive, whoever starts organizing help, organizes help. Fights for leadership are usually worse than sub-optimal leadership - unless it violates point 1.

No help is usually worse than bad help. More people dies because no one dared to check their airways, than people who gets paralyzed because someone did check the airways.

If there's an imminent danger, like fire, of you don't know if there is but for any reason you suspect there might be, use reverse triage - help those, who require least help to get to safety. Also, see point 1.

If they scream, they breathe. The ones that don't scream probably need your help more. Unless it's point 5. situation.

Don't move people you don't have to move. Don't hesitate to move people you do have to move. For example, resuscitation only really works on hard flat surface. Broken bones can be treated later, death can't. Paralysis might happen if you move someone to do it, but death will happen if you won't.

If you don't know what to do, do what you know, or ask somebody. If you can't help directly, because of point 1. or anything else, you can go and find a way for responders to get ambulances close, for example. Or you can stay back and not get in the way of people who knows what they should do. Nobody will think less of you for that!

You might find reading Stewart Brand's essay on his learnings from the 1989 Loma Prieta earthquake, Learning from the 1989 SF EARTHQUAKE, originally published in the Coevolution Quarterly.
After university, Stewart Brand was a US Army infantry officer,  founded the Whole Earth Catalog back in the late 1960s, and was one of Ken Kesey's Merry Pranksters. His is, you might say, a deep thinker.
As it happened, Stewart Brand was driving through the Marina District when the Loma Prieta earthquake occurred. San Francisco's Marina District is/was a neighborhood built on fill. Lots of frame buildings. When the 'quake hit, the  underlying soil pretty much liquified.
As a human being, he stopped and rendered aid. One of his takeaways from the experience was that in a disaster, certainly at the beginning, leadership is AWOL. People are panicked and don't know what to do. Brand's training as an infantry officer helped him fill in the gaps and helped him get people organized and tell them what to do.


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Does a history of social anxiety significantly damage commercial pilot career prospects?
Yeah, I've had a history with social anxiety although it's all sorted now because I got therapy. I was wondering if it's important that I disclose this to employers or just lie if asked? Would they be able to find out? And yeah, if I did disclose this would it harm the chances of me achieving my dream of being a commercial pilot?
I ask this as I know people with a history of depression aren't meant to be commercial pilots.

Related: Will having a history of depression prevent me from flying? The answer is probably the same: talk to an AME.

Leaving aside the moral aspects, the truth is that most pilots make only 'limited disclosures' when filling up their medical questionnaires, since they all wish to continue flying, either as professionals or for pleasure. People are prisoners of what they say, and masters of what they hide...

I don't know about the question in your title, but I can answer the question in the body:

I was wondering if it's important that I disclose this to employers or just lie if asked?

No, you should not lie about your medical history. If you knowingly lie about your medical history, and it subsequently comes out, it could cost you your career - including the tens of thousands of pounds (or euros or dollars) you spent on getting your CPL or ATPL. Even if you have insurance against losing your medical certificate, they almost certainly won't pay out in this case, leaving you with a debt bigger than a student loan and no job to pay it off. It'll also make it much harder to get a medical certificate in future and return to flying status.
Worse yet, if the reason this comes out is because of an accident, you may face a criminal investigation because you flew knowing that your medical certificate was not valid, regardless of whether you think your condition could have contributed. You can't expect your employer (ex-employer) to stand up for you in this case.
Although I have a class 2 medical in the UK, I'm no expert in the medical requirements. It would surprise me if a past mental health condition which doesn't really affect your ability to fly, and which was successfully treated without medication, would stop you getting even a class 1 medical. It would probably just mean more uncomfortable questions in the medical exam, and probably having to get a written opinion from the psychiatrist who treated you. That might cost you some time and cash in the short term, but it's worth it to know it won't come back to haunt you later.

more uncomfortable questions - level of effect of the therapy the OP mentions may be very well subjectively judged by how much or how little the corresponding questions evoke.

@Dan Hulme provides a solid answer and I'll expand a bit for the US.
As mentioned in @fooot's comment, you really need to talk to an AME about this. Only an AME can give you an answer to this and no one on a forum can legally decide this for you. There are some other things you should be aware of:
While you may only need a Class II medical to fly commercially in the States, you may or may not be free to use whatever AME you like. The airline may have its own doctors it uses to check you out above your standard medical check. Remember, the legal certifications only allow you to have the job; they do not guarantee it. Keep in mind, you can go to any AME to get your medical for the license itself, as legally you only need an AME to approve you.
You should of course never lie on a job application - especially in this case considering what you want to do. However you should be aware of what employees can access and what they can not in terms of medical records. You should make yourself aware so you are not unfairly disqualified (not so you can maliciously skirt the rules).
In the States you can't necessarily get fired if such information comes to light unless is violates the company's policies (and you lied to get in) or it was deliberately suppressed.
You can read the full guide for AMEs if you are interested.
The FAA also has a short FAQ about Pilot Medical Certification.


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How can I land without any propulsion? Was the Microsoft simulator right?
Many years ago I played with Microsoft Flight Simulator, turning off my engines and trying to land the plane.  Coming down too steeply would crash, as would coming down too slowly. So I figured out the right attitude (angle of descent) to successfully stay in flight until reaching ground level.
Actually landing was another puzzle to solve. I had to "swoop" in—that is, just before landing, descend steeply for a short time to pick up velocity, then use that stored energy to glide in and land.
Was this realistic at all? Are there any changes that need to be made to the overall abstract process?

What kind of plane?

@GregHewgill -- Wish I could remember. That was 1987-89. Do you happen to know what the choices were?

@GregHewgill:  Someone using MSFS in '87–'89 would most likely have been flying a simulated Cessna 182. That was the default choice, though a Learjet 25G or a Sopwith Camel were also available.

OT: I remember flying Chuck Yeager's SR-71 Blackbird into space with very long flights at a very low rate of climb.

As a point of information, I was once called to dinner and left MSFS running in the '85-87 era, to find on return that the plane had landed itself. /However/, my recollection is that I was using a glider ("sailplane" etc.), and even if the software was prepared to waft that down gently it doesn't mean that it would have behaved the same for another type of aircraft. I'd add that in "real life" I believe there's been at least one case where an airman ejected from an uncontrollable fighter, which later recovered and grounded itself with only moderate damage.

@MarkMorganLloyd:  That would be the "Cornfield Bomber".

Im surprised no one has yet posted real life examples - for example, the Gimli Glider, a 767 which lost both engines due to fuel exhaustion at cruising altitude, glided to a successful landing - https://en.wikipedia.org/wiki/Gimli_Glider Or Air Transat Flight 236, an A330 which again lost both engines at cruising altitude due to fuel exhaustion, glided for over 120KM to a successful landing https://en.wikipedia.org/wiki/Air_Transat_Flight_236

@Moo Or in more recent memory, the miracle on the Hudson.

Pilots of single-engine aircraft practice this kind of thing all the time, indeed it's a requirement to do it in most flight tests to actually get the licence/certificate.
There is a certain airspeed on every aircraft known as the best glide airspeed. This airspeed delivers the best lift to drag ratio, the end result being you will glide a further distance than you would at any faster or slower speed. You can maintain speed without engine power by pitching the nose down, and vice versa to slow down.
As for the actual landing itself, the swoop procedure you describe is not necessary as there is already enough energy at the best glide speed, so you can just flare as normal. For example, the Piper aircraft I fly has a best glide speed of 73kts (this can vary with weight and conditions), but the normal approach speed without flaps is 70kts anyway.
Twin engine jet pilots don't practice this as the likelihood of it happening is so remote, but the principles are largely the same.

And, just to be clear, when pilots of single-engine aircraft practice this they don't shut off the engine. They set it the throttle to idle; that way, if they come up short of the runway they can recover.

You might want to be more specific about what you mean by "this kind of thing".  I think you mean engine out scenarios, but given that the question is about the landing swoop, it initially seemed like you meant that.

This is not realistic for most scenarios.  Every airplane has at least a published “best glide” speed that provides the best glide distance horizontally for the amount of altitude lost.  My airplane has a glide ratio of just over 9:1 at this speed, so if I am 3,000 feet above the ground, I can under ideal conditions glide 27,000 feet, or just under 5 statute miles.
There’s a slightly different speed that maximizes time aloft.  In other words, there’s a speed at which I won’t glide quite as far a distance, but I will be aloft longer.  Most of our training focus is on maximizing distance (getting to a favorable spot) over maximizing time (having more time to diagnose.)
My airplane’s best glide ranges from 70 to 80kts indicated, depending on weight.  On my typical mission it’s about 77 at takeoff and about 73 at landing weight.  If it’s 77, I am going to trim the airplane up to fly right at 77 all the way to my desired landing point, and will maneuver around to arrive at a final approach position a bit high by gliding around at 77, not by altering my speed.  I can use flaps and/or slip maneuvers to steepen my descent angle while sill maintaining a pretty consistent glide speed.
There should be no “zooming” or swooping, with rare exceptions.  I want to bleed off the last speed—from 77 down to my touchdown target speed of about 55 kts—as I am on my last couple of hundred feet of descent.  The goal is always to just do a very normal landing approach and flare, essentially the same as a “normal” landing, whenever possible.
There is no speed you can get down to that makes crashing upside-down at that slower speed better than crashing right-side-up at the higher speed.  So hitting whatever you are going to hit at, or just above stall speed, is profoundly more survivable than stalling trying delay the inevitable forced landing another second or two.

What causes upside-down crashing?

@JeremyFriesner Stall and a  spin or spiral.

I think to say this is "not realistic" is incorrect. Your answer provides the correct procedure to land in such a situation, but that doesnt mean Flight Simulator was unrealistic. What the OP described would also happen in real life if you chose to land that way. "Not recommended" or "not the correct procedure" would be better wording.

@GavinCoates: I would think even if such an approach wouldn't generally be recommended, it might nonetheless represent the "least evil" among available options.  If one has an engine failure and there's an open runway nearby, and one has too much energy to fly a stabilized approach, but not enough energy to fly a 360 degree circle to bleed off energy, an unstabilized approach to the runway might be better than a stabilized approach that lands off the runway.

I read this question as "Is the simulator accurately modeling the behavior of the aircraft" To which I think the answer would probably be "to a reasonable level of fidelity, yes".
There is a follow up question about your technique, which has been answered, and to which I'll add.  The generally accepted technique for an engine failure scenario, as well as several other types of emergencies, are outlined in chapter 18 of the current version of the FAA's Airplane Flying Handbook (FAA-H-8083-3C).  These procedures get further refinement, typically including airspeeds to use, in the operating handbook for individual aircraft.
It the case where you had to dive near the end of your descent, it may have been that your low airspeed corresponded to a high angle of attack and high descent angle.  It is reasonable to expect this flight condition to be well modeled in your simulation.  This condition would indeed result in a sub-optimal glide, and would also require increasing the airspeed in order to arrest the descent rate.

That is how I read the question too - I think this is the only answer that accurately answers what the user was asking. he wasnt asking what the correct procedure would be in the situation described, but whether what he experienced in FS would also be experienced in real life if you did the same thing.

In 1987-9, computers of the age were more than capable of getting the math and physics right on flight simulation.  Graphics fidelity was another matter :)
It is perfectly ordinary for pilots to be all over the map with airspeed and descent rate as you did.  They may be trying to get enough airspeed across the prop to attempt a "windmill start". They may be tuning for best glide.  They may be slewing or otherwise deliberately scrubbing off energy in order to arrive at the target landing site with enough energy but not too much.
In fixed-wing aircraft, energy is stored in two forms: airspeed (kinetic) and altitude (potential).  Flight is all about trading one for another, and there's nothing magic about the trade - you can't create more energy than you had, nor destroy it merely by trading.  Although...  I hear some airplanes have an "engine" that can add new energy  :)
This energy arbitrage was exactly what you were doing, and that's what it's all about.
If you arrive at the runway stripes with too much energy, you will either be too fast or too high in the sky.  And you could find yourself in an "impossible turn" situation where your surplus is not enough to get lined up on a runway before you run out of energy.
So whatever you were doing to get on the ground, it was working :)

that said, MSFS back then, and AFAIK to this day, places the aircraft on rails rather than modelling actual aerodynamics. This leaves it with inadequate behaviour in certain corner cases, and this would likely be one such. X-Plane handles things better.

While I have not audited available information thoroughly, MSFS 4.0, according to Wikipedia, was released in 1989 had an aircraft editor which allowed the user to alter paramaters such as frontal area, aspect ratio, etc. giving some clues about it's underlying aerodynamic model.  Xplane appears to be more sophisticated; I believe it "bakes" a panelized model into easier to compute coefficients. On the other hand, I think saying that MSFS is/has been "on rails" is giving it short shrift.

I just took another look at x-planes brag sheet on its model, which reminds me that they don't bake the panel model into a set of stability derivatives, but run the simulation on a somewhat simplified (10 elements per side) panel model.  This is much more sophisticated than what is probably common, however, in the context of this question, this simpler models will be more than adequate.

authors: Vladimir F Героям слава


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Am I allowed to tell ATC "unable" if asked to climb to less than 12,500 ft without supplemental oxygen aboard?
So, 91.211 says I'm not allowed to fly above 12,500 ft without supplemental oxygen.  I'm less clear if all planes with a service ceiling above that line are required to have the oxygen aboard in the first place.
For reasons of handling equipment failures, I presume that, regardless of the requirement to have it aboard, if I don't have it and ATC says "Climb and maintain one-tree thousand," I respond "Unable, no oxygen aboard."
But what happens if I'm only asked to climb to 10,000 ft - or even 8,000 ft (altitudes where hypoxic effects, though minor, have been observed) and while I recognize the legality of the operation I'm not - as PIC - comfortable with the risk?
Am I allowed to respond with "Unable" or do I have to request a lower altitude and hope ATC is feeling cooperative?

Related: https://aviation.stackexchange.com/q/11909/54557, https://aviation.stackexchange.com/q/7915/54557

If you are healthy 8-10k' shouldn't be an issue.

@757toga, interesting, I didn't know that.  It definitely improves vision though!

Cabin pressurisation in airliners is usually 8,000 feet - https://en.wikipedia.org/wiki/Cabin_pressurization#Aircraft

@DaveGremlin That's part of why I used 8,000 as the floor here.

@MichaelHall - There are a lot of fat and unhealthy pilots out there.

"Am I allowed to respond with "Unable"" AFAIK the pilot can always tell ATC they can't/won't comply if they have any doubt about the safety of complying. The safety of your passengers, crew and vehicle is always more important than commands of ATC and properly communicating this will improve the likelihood of a satisfactory outcome for everyone.

Well, for someone in very ill health, or with one lung, even 4K' unpressurized might stress them medically.  My point is, if asked to climb to 8'K and you respond "unable due to no O2", the controllers probably won't challenge you, but they may exchange quizzical looks between themselves.  (not that you should care...)  Certainly don't file for any higher than you are comfortable flying.